Re: [PATCH v4 1/2] dt-bindings: hwmon: Add starfive,jhb100-fan-tach

[Conor Dooley]

On Sat, Aug 29, 2026 at 06:19:40PM -0700, Changhuang Liang wrote:
> Add compatible "starfive,jhb100-fan-tach" for StarFive JHB100 Fan-Tach
> controller.
> 
> Signed-off-by: Changhuang Liang <changhuang.liang@xxxxxxxxxxxxxxxx>
> ---
>  .../hwmon/starfive,jhb100-fan-tach.yaml       | 93 +++++++++++++++++++
>  1 file changed, 93 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml b/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml
> new file mode 100644
> index 000000000000..1dcd4932768f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/hwmon/starfive,jhb100-fan-tach.yaml
> @@ -0,0 +1,93 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/hwmon/starfive,jhb100-fan-tach.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: StarFive JHB100 Fan-Tach controller
> +
> +maintainers:
> +  - Changhuang Liang <changhuang.liang@xxxxxxxxxxxxxxxx>
> +
> +description:
> +  The StarFive Fan-Tach controller can support up to 16 fan tach input.
> +
> +properties:
> +  compatible:
> +    enum:
> +      - starfive,jhb100-fan-tach
> +
> +  reg:
> +    maxItems: 1
> +
> +  clocks:
> +    maxItems: 1
> +
> +  resets:
> +    maxItems: 1
> +
> +  interrupts:
> +    maxItems: 1
> +
> +  "#address-cells":
> +    const: 1
> +
> +  "#size-cells":
> +    const: 0
> +
> +patternProperties:
> +  "^fan@[0-9a-f]+$":
> +    $ref: fan-common.yaml#
> +    unevaluatedProperties: false
> +
> +    properties:
> +      reg:
> +        description:
> +          PWM channel index. The driver allows two fans to share the same
> +          PWM channel, or each fan to use a dedicated channel.

Doesn't matter what the driver can do, the description should describe
what the hardware supports.
pw-bot: changes-requested

Does this fan-tach controller provide the PWMs?
If so (although Guenter may correct me), I think the fan-tach controller
needs to be.

If you don't do that, I think you're going to run into problems with
having multiple nodes with the same unit address when two fans share a
pwm?

I think what you're supposed to do is drop "reg" and replace it with
"pwms", but once again Guenter may correct me there.
e.g. aspeed,g6-pwm-tach.yaml

Cheers,
Conor.

> +        maximum: 15
> +
> +      tach-ch:
> +        description:
> +          The tachometer channel(s) wired to the fan(s) driven by this PWM
> +          channel. Integer values in the range 0-15.
> +        minItems: 1
> +        maxItems: 2
> +        items:
> +          maximum: 15
> +
> +    required:
> +      - reg
> +      - tach-ch
> +
> +required:
> +  - compatible
> +  - reg
> +  - clocks
> +  - resets
> +  - interrupts
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    fan-controller@11be0000 {
> +        compatible = "starfive,jhb100-fan-tach";
> +        reg = <0x11be0000 0x400>;
> +        interrupts = <128>;
> +        clocks = <&per2crg 33>;
> +        resets = <&per2crg 5>;
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        fan@0 {
> +            reg = <0x0>;
> +            tach-ch = /bits/ 8 <0x0 0x8>;
> +            pulses-per-revolution = <2>;
> +        };
> +        fan@1 {
> +            reg = <0x1>;
> +            tach-ch = /bits/ 8 <0x1>;
> +            pulses-per-revolution = <2>;
> +        };
> +    };
> -- 
> 2.25.1
>

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